New cases of super-flares on slowly rotating solar-type stars and large amplitude super-flares in G- and M-type main-sequence stars

TL;DR

This study reports new super-flare detections on slowly rotating Sun-like stars and large amplitude super-flares on G- and M-type stars, suggesting the Sun might also produce rare super-flares, with analysis of flare decay times and energies.

Contribution

It presents new detections of super-flares on slowly rotating Sun-like stars and large amplitude super-flares on G- and M-type stars, using improved methods for estimating flare energies.

Findings

Super-flares found on 13 slowly rotating Sun-like stars.

Large amplitude super-flares detected on G- and M-type stars.

No large-amplitude flares observed in A, F, or K stars.

Abstract

In our previous work, we searched for super-flares on different types of stars while focusing on G-type dwarfs using entire Kepler data to study statistical properties of the occurrence rate of super-flares. Using these new data, as a by-product, we found fourteen cases of super-flare detection on thirteen slowly rotating Sun-like stars with rotation periods of 24.5 to 44 days. This result supports earlier conclusion by others that the Sun may possibly have a surprise super-flare. Moreover, we found twelve and seven new cases of detection of exceptionally large amplitude super-flares on six and four main-sequence stars of G- and M-type, respectively. No large-amplitude flares were detected in A, F, or K main-sequence stars. Here we present preliminary analysis of these cases. The super-flare detection, i.e. an estimation of flare energy, is based on a more accurate method compared to previous studies. We fit an exponential decay function to flare light curves and study the relation between e-folding decay time, $\tau$, vs. flare amplitude and flare energy. We find that for slowly rotating Sun-like stars, large values of $\tau$ correspond to small flare energies and small values of $\tau$ correspond to high flare energies considered. Similarly, $\tau$ is large for small flare amplitudes and $\tau$ is small for large amplitudes considered. However, there is no clear relation between these parameters for large amplitude super-flares in the main sequence G- and M-type stars, as we could not establish clear functional dependence between the parameters via standard fitting algorithms.